JPS6348862A - Manufacture of heterojunction bipolar transistor - Google Patents

Abstract

PURPOSE:To form a base electrode readily even in a minute external base region in a self-aligning method, by forming the base electrode at a part very close to the junction part of a collector and a base, thereby reducing the resistance of the external base to a remarkably small value. CONSTITUTION:With a temporary collector 13 as a mask, etching is performed to a layer 4 for forming a base by a wet etching method. A collector region comprising a collector 5-a and a cap layer 6-a is formed. Both sides of the region along the extending direction of a stripe are formed in an inverted mesa shape. The entire surface of the upper part of the collector region is covered with a collector electrode 8. The collector electrode has an umbrella shape, i.e., an undercut part, which is formed by etching at the lower part of the collector electrode. A mask is applied on a part other than parts including both ends of the stripe and a base-electrode forming part. Base electrode metal is evaporated and lift-off is performed. Thus a base electrode 9 is formed. In this way, the base electrode 9 is formed at a part very close to the collector electrode at the peripheral part directly beneath the umbrella of the collector electrode metal.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of Industrial Application The present invention relates to a method for manufacturing a heterojunction bipolar transistor (hereinafter referred to as HBT), which is promising as an ultra-high speed and ultra-high frequency transistor.

Conventional technology In recent years, HBT, which uses a semiconductor material with a larger bandgap than the base as the emitter of a bipolar transistor (hereinafter referred to as BT), has been actively researched as one of the promising candidates for ultra-high speed and ultra-high frequency transistors. It's getting worse.

FIG. 6 shows the structure and manufacturing method of a conventional HBT.

1 is a substrate, 2 is a highly doped semiconductor material layer of the same type as the emitter to facilitate the formation of an ohmic contact with the emitter, 2-a is an emitter electrode extraction region, and 3 is a semiconductor material layer for forming the emitter region. , 3-a is an emitter region, 4 is a semiconductor material layer for forming a base region, 4-a is a base region, 4-b is an external base region for taking out a base electrode, and 5 is for forming a collector region. 5-a is a collector region; 6 is a highly doped semiconductor material layer of the same type as the collector to facilitate the formation of an ohmic contact with the collector; 5-a is a collector cap layer above the collector region; , 7 is a multilayer structure material formed from the semiconductor material layers 6 to 6, 8 is a collector electrode, 9 is a base electrode, and 10 is an emitter electrode. Multilayer structure material 7 epitaxially formed on substrate 1
(FIG. 6(a)), by photolithography and etching, as shown in FIG. 6fbl, 6-a
and 5-b, a base region 4-a and 4-b, an emitter region 3-b, and an emitter electrode extraction region 2-a.

Then, as shown in FIG. 6 (C1), a collector electrode 8, a base electrode 9, and an emitter electrode B110 are formed.

The operation of the HBT configured as above will be explained.

f, which is an indicator of high-speed operation of HBT, and f.

is expressed as follows.

't''1/2π(τ8+τ8+τ0+τ..)Here,
τB (emitter depletion layer travel time)-)'E (CB
("CB B 10p B), τB (Base strike time) - W82 /πDB, τ. (Collector depletion layer strike time) - W./2■s, τ. (Collector depletion layer charging time) - ( R88+Ro) (cB.

+CPC)'R8 is the base resistance, CF3c is the base-collector capacitance, C, 38 is the base-emitter capacitance, C
PB is the base layer stray capacitance, C2゜ is the collector layer stray capacitance, WB is the base layer thickness, DB is the base layer diffusion coefficient, W
C is the thickness of the collector depletion layer, Vs is the collector strike velocity,
R8B is an emitter contact resistance, and Ro is a collector electrode.

HBT uses a semiconductor material with a larger bandgap than the base as the emitter to suppress leakage of holes from the base to the emitter (in the case of n p n type). The emitter and collector can be lightly doped. This makes it possible to reduce the base resistance RB, which is important for increasing the speed and frequency of transistors, so fI
ll becomes larger. Furthermore, in general in BT, Kai.

. C8o is a factor 08B(n,
h), CB(, (n, h) and junction area AEB.

It is expressed as a product of ABC. In HBT, the emitter and collector are lightly doped and the base is highly doped, so CE8 (n, h), C8C (n.

h) depends only on the emitter-collector doping, and CBB and CBo are as follows.

Therefore, HBT has CP and 8° CB compared to normal BT.
Since C becomes smaller, τ8. As τCG becomes smaller, it becomes possible to increase ft. Furthermore, since CEB becomes small, it becomes possible to increase f and n in combination with the above-mentioned small R8.

Thus, HBTs are inherently advantageous for higher speeds due to their heterostructure. However, in order to further increase the speed, it is important to miniaturize the device structure in addition to this. For example, by reducing the base-collector junction area ABC, C
Decrease BC, thereby f. to increase the
It is very important to increase f by reducing the resistance of the external base region (external base resistance).

Problems to be Solved by the Invention However, with the structure and manufacturing method as shown in FIG. It was extremely difficult to form the base ift scratches 9 on top. Furthermore, in order to reduce the external base resistance, it is nearly impossible to form the base electrode several thousand people close to the collector-base junction using normal mask alignment.

In view of the above-mentioned problems, the present invention allows the base electrode 9 to be formed extremely close to the collector-base junction, thereby significantly reducing the external base resistance and increasing the rm.
The present invention aims to provide a new method for manufacturing HBT that can produce T.

Means for Solving the Problems In order to solve the above problems, in the HBT of the present invention, H
Using a multilayer structure formed by epitaxy after BT formation, a striped protrusion consisting of a highly doped camp layer provided on the top of the collector or a layered structure of a collector and a collector cap layer is provided, and the striped protrusion is Both sides of the side surfaces along the direction of extension are substantially vertical, one side is substantially vertical and the other side is in the shape of an inverted mesa, or both sides are in the shape of an inverted mesa, and at least on both sides of the striped projection in the direction of extension. A material whose upper surface can be selectively removed with respect to the collector electrode, the base electrode, and the heterojunction bipolar transistor forming material after the step of forming the striped protrusion having the collector electrode metal protruding in an umbrella-like manner or after the step. The upper surface of the collector electrode metal and the upper surface of the base electrode extraction area are removed using an anisotropic dry etching method to remove the side wall of the collector electrode and the collector side wall portion protruding in the striped form. a step of forming a side wall made of a protective film made of the above material, a step of forming an external base region, and a step of depositing a base electrode metal from above to form a cap of the collector electrode metal or a collector electrode metal having the side wall. The base electrode is formed very close to the collector-base junction by at least the step of forming the base electrode on the periphery directly under the umbrella.

Function: In the method for producing HBT of the present invention, HBT of minute size is produced.
However, the base electrode can be easily formed very close to the collector-base junction in a self-aligned manner. Therefore, the external base resistance becomes extremely small, which is extremely effective in reducing the base resistance R8. This has a remarkable effect on increasing f.

EXAMPLE Hereinafter, a method for manufacturing a heterojunction bipolar transistor (HBT) according to an example of the present invention will be described with reference to the drawings.

Example 1 FIG. 1 shows an example of the method for manufacturing an HBT of the present invention. As shown in FIG. 1(a), on a (001) GaAs substrate 1, a highly doped GaAs (
n''-GaAs) layer 2, n-type AIXGa,, As(N-AIXGal-
XAs) 1i3, P-type Q forming the base region
an aAs (p-GaAs) layer 4, an n-type GaAs (n-GaAs) layer 5 for forming a collector region,
Highly doped n-type GaAs (n”-GaAs) to facilitate the formation of collector ohmic contacts
The layers 6 are epitaxially formed in this order to form the multilayer structure material 7.
Then, a SiOx protective film 11 made of a material that can be selectively removed with respect to the underlying 04''-GaAs by wet etching and is not substantially attacked by wet etching is provided thereon, and a collector is formed on it. A temporary collector of metal A1 is provided in a portion corresponding to the area so that the stripe extension direction is in the <110> direction, and then anisotropic dry etching is performed using the temporary metal collector as a mask. As shown in Figure 1), S
A temporary collector 13 made of an iox protective film 11 and metal Al 12 is formed. Next, as shown in FIG. 1 (el), using the temporary collector 13 as a mask, the layer 4 for forming the base is etched by wet etching to form a collector with an inverted mesa shape on both sides along the extending direction of the stripes. 5-a and a cap Ji 6-a. Next, as shown in FIG. The temporary collector is removed by etching, and a recess 15 is formed as shown in FIG. An umbrella-shaped collector electrode is formed which covers the entire upper part of the region and has an undercut part by etching at the lower part of the collector 1Iis.Then, as shown in FIG. 1(g), a base mesa and a base mesa are formed by photolithography and etching. An emitter region is formed, and an emitter electrode is formed.Then, a portion including both ends of the stripe and a base electrode forming portion are masked, and the base electrode metal is evaporated and lifted off, as shown in FIG. A base electrode 9 is formed.

As a result, the base electrode 9 is formed at the periphery immediately below the cap of the collector 1ilt metal at a very close distance to the collector-base junction. Further, since the sidewalls along the extending direction of the stripes have an inverted mesa shape, when a vapor deposition beam with good linearity is used, the base electrode will not be short-circuited with the collector.

Example 2 FIG. 2 shows the side wall 15 of 1g shown in Example 1 (after forming the phantom structure, sloxl is formed on the striped protrusion).
-a is provided to prevent the vapor-deposited metal from wrapping around the side wall portion of the collector due to vapor deposition during the formation of the base electrode, thereby preventing short circuits. First, cover the entire surface with a thin 5tyx thin film 16 as shown in Figure 2 (ta+), then remove Siox from the upper part of the collector and the part where the base wire is taken out by anisotropic dry etching. Like S i
A side wall 16-a made of ox is formed. Next, the base electrode 9 is formed by the method shown in Example 1, and then,
5iOxL6-a on the side wall was removed by etching,
By this method, the base electrode metal is removed by wrapping around and adhering to the side wall of the collector, thereby preventing a short circuit between the collector and the base electrode. Even in the case of a evaporation beam with poor linearity, the base electrode can be formed without any problem. 3 In FIG. 3, the extension direction of the striped temporary collector 13 is set to <1 in the multilayer structure material 7 shown in FIG.
00> direction. In this case, the walls on both sides along the extending direction of the stripe and the walls at both ends of the stripe are etched by wet etching using the temporary collector 13 as a mask. As shown in Figure Fa+, substantially vertical striped protrusions are formed.

Next, by converting the temporary collector into a collector electrode using the same method as in Example 1, the collector electrode formed on the upper part of the striped collector region protrudes into the peripheral part of the stripe by undercutting by wet etching. The umbrella-shaped collector electrode is shown in Figure 3 ('b).
It is formed as follows. Using this, the base electrode 9 is formed as shown in FIG. 3+C1 by the same method as in Example 1. However, in this case, since the bulk of the collector electrode is formed in the entire peripheral area of the stripe, Example 1
It is not necessary to cover both ends of the stripe as in the case of .

Example 4 FIG. 5 shows that after forming the structure of FIG. 3 (bl) shown in Example 3, the structure of FIG.
The surface of the material having the structure shown in FIG. 3 (al) is covered with SiOx thin H15 as shown in FIG. Form it like this. Using this, base electrode metal is formed by vapor deposition and lift-off, and then 5tyx￥
The side wall 16-a of the i4 film is removed by etching to remove the metal attached to the collector side wall to prevent the base electrode from shorting with the collector. Even in the case of Example 4, if a deposition beam with good linearity is used, the base electrode will not be short-circuited with the collector. It becomes effective.

Example 5 In Example 1, instead of forming a temporary collector on the multilayer structure material 7, a collector electrode 8 made of A u G e / A u is formed as shown in FIG. 5 fat, and this is masked. Etching is performed up to N4 to form a base, and both sides of the stripe along the direction of stripe extension form an inverted mesa shape, covering the entire upper surface of the stripe, and forming a cap from the sides along the direction of extension of the stripe. The protruding collector electrode 8 is formed as shown in FIG. 5 (bl).The base electrode is then formed using the same method as in Example 1.

Although an example has been shown as a method of etching using the collector electrode metal 8 as a mask, this example can also be applied to cases corresponding to Examples 2 to 4.

In the method of using the temporary collector as a mask shown in Examples 1 to 4, S is used as a mask in contact with the underlying semiconductor material.
Although iOx is used, S iox and 3 iNx can be used as general materials that can be selectively removed with respect to the underlying semiconductor material. Further, when the base is a compound semiconductor material, Ge or Si can be used as the temporary collector, and when the base semiconductor material is Ge or Si, the compound semiconductor material can be used as the temporary collector. This method has the advantage of being able to be combined with processes that require heat treatment, such as ion implantation, by selecting 5i0x, SiNx, or other materials that do not react with the underlying material during heat treatment as the temporary collector.

In the method of using the collector electrode as a mask shown in Example 5, it is necessary to select a metal material that will not be corroded by the etching solution during wet etching of the underlying semiconductor material. In addition, by selecting a metal material that does not react with the underlying semiconductor material during heat treatment, it can be combined with processes such as ion implantation that require heat treatment.

In Examples 1 to 4, the temporary collector 13 is used as a mask to etch down to Fi4, which forms the base.
After etching the layer forming the collector halfway and performing a process involving heat treatment such as ion implantation, the collector electrode 8 is formed, and then, after exposing the external base layer by etching, the method of the embodiment is applied. You can also do that.

Using the temporary collector 13 as a mask, etching is performed to the layer that will form the collector to form striped protrusions mainly consisting of a highly doped cap layer, and then ion implantation is performed to form the external base region of the layer that will form the collector. It is also possible to transform the portion corresponding to the region into an external base region by ion implantation, form the collector electrode, and apply the method of the embodiment.

In Examples 1 to 4, the base electrode is formed after changing the temporary collector to the collector electrode, but with the temporary collector attached, the temporary collector's umbrella or the temporary collector and the striped collector are formed. It is also possible to form a base electrode by using a temporary collector whose sidewalls are provided with a SiOx thin film.

In Examples 2 and 4, a SiOx thin film is used as the material for forming the striped protrusions and the sidewalls of the collector electrode. and other materials can be used.

In Examples 1 to 5, G was used as the HBT forming material.
a As A I! X G a I-X A
Although s-based zinc blend materials are used, the examples can also be applied to other zinc blend materials. Furthermore, the method of this embodiment can also be applied to the production of an HBT using a multilayer structure material consisting of a zinc blend material and a diamond material such as Ge or St.

In Examples 1 to 5, epitaxy was formed (100)
Although a striped collector region is formed on the surface, other epitaxially formed surfaces can also be used. For example, in the in-plane <110> direction of a multilayer structure material created by epitaxial formation on the (211) plane of a zinc blend or diamond structure type crystal,
The striped protrusions of the collector can be provided so that their extending directions coincide. In this case, one (
11k) plane parallel to the stripe and perpendicular to the plane, one (1
11) Since the planes are parallel to the stripes and are located in an inverted mesa shape, it is possible to form a striped collector in which one side on both sides along the extension direction is perpendicular and the other side is in an inverted mesa shape. Therefore, an umbrella-shaped collector electrode can be formed in the same way as in the cases shown in Embodiments A to 4. As described above, in the manufacturing method of the present invention, as shown in the examples, a stripe of a collector with substantially vertical or reverse mesas on both sides along the elongation direction is produced using a (100) grown multilayer structure material. In addition to forming protrusions, we also use multilayered materials grown in various crystal orientations to create striped protrusions that are perpendicular on both sides in the direction of stripe extension, inverted mesa, or in which one side is perpendicular and the other is an inverted mesa. The present invention can also be applied to the case where a collector region is formed to form an umbrella-shaped collector electrode.

Effects of the Invention As described above, the present invention provides an HBT in which a semiconductor material having a larger band gap than the base is used for at least the emitter and the collector, and the collector is provided above.
In the process of forming the HBT from a multilayer structure material formed by epitaxy, which is the source of HBT formation, a highly doped semiconductor material layer provided on the upper part of the collector or a striped protrusion made of a layered structure of the collector and the highly doped layer is formed. Both sides of the striped protrusion along the extending direction are substantially vertical, one side is substantially vertical and the other side is in an inverted mesa shape, or both sides are in an inverted mesa shape, and the stripe covering the entire upper part of the protrusion, and
A step of forming the stripe-like protrusion having a collector electrode metal protruding like an umbrella on at least both sides along the extension direction of the stripe-like protrusion, or after the step, forming the upper surface of the material as a collector electrode and a base. The electrode and HBT forming material are covered with a protective film made of a material that can be removed in ashes, and the upper surface of the collector electrode metal and the upper surface of the base electrode extraction area are removed using an anisotropic dry etching method. a step of forming a protective film made of the material on the side wall of the collector electrode metal and a side wall of the collector portion protruding from the upper surface; a step of forming an external base region; depositing the base electrode metal from above; A manufacturing method is used which is characterized by having at least the step of forming the base 1 as a pole on the m-side portion directly under the umbrella of the collector electrode metal or the collector electrode metal and the side wall.

As a result, the base electrode can be easily formed in a self-aligned manner even in the minute external base region, which has extremely large process advantages.In addition, the base electrode can be formed very close to the collector-base junction. Because you can
The external base resistance of the HBT can be significantly reduced, thereby r. A large HBT can be produced.

[Brief explanation of drawings]

1 to 5 are process diagrams showing the manufacturing method of 1 (BT) of the present invention, and FIG. 6 is a process diagram showing the conventional HBT manufacturing method. ■...Substrate, 2.・・・Highly doped layer to facilitate formation of emitter ohmink contact,
2-a...Emitter electric scraping area, 3...
...semiconductor material layer for forming an emitter region,
3-a... Emitter region, 4... Semiconductor material layer for forming base region, 4-a...
... Base region, 4-b ... External base M region for taking out the base electrode, 5 ... Semiconductor material layer for forming the collector region, 5-a ...・・・
Collector region, 6...Highly doped layer for facilitating formation of collector ohmic contact, 6-a
・Old...Collector cap layer at the top of the collector, 7...
...Multilayer structure material formed by epitaxy, 8...
... Collector electrode, 9 ... Base electrode, 10.
... Emyn taffeta, 11 ... Protective film layer for forming a temporary collector, 12 ... Metal layer for the temporary collector portion, 13 ... Temporary Collector, 14...Photoresist, 15...
A recess formed in the collector portion of the photoresist 14, 16... Protection for forming a collector electrode and a side wall of the collector region, 16-a... Formed from the protective film 16. Collector electrode and sidewall of collector region. Name of agent: Patent attorney Toshio Nakao 1 person 1g 1 diagram
11 Substrate 1 Fig. 15 No. 4 3 - Emitter '8 failure/6 - Side wall type reverberation Fig. 3 Fig. 4 Fig. 8-11 Collector electrode Fig. 5 ε Fig. 6

Claims (7)

[Claims] (1) A multilayer structure material in which a heterojunction bipolar transistor is epitaxially formed on a substrate, using a semiconductor material with a larger band gap than the base for at least the emitter of the bipolar transistor, and the collector is provided above. A highly doped semiconductor material layer provided on the upper part of the collector or a striped protrusion made of a layered structure of the collector and the highly doped layer, the striped protrusion being formed in the direction in which the striped protrusion extends. Both sides of the side surface along the stripe are substantially vertical, one side is substantially vertical and the other side is in an inverted mesa shape, or both sides are in an inverted mesa shape, and the stripe-like protrusion covers the entire upper part of the striped protrusion, and After the step of forming the striped protrusion having collector electrode metal protruding like an umbrella on at least both sides of the striped protrusion along the extension direction, or after the step, the upper surface of the material is formed into a collector electrode, a base electrode and a heterojunction. The bipolar transistor forming material is covered with a protective film made of a material that can be selectively removed, and the upper surface of the collector electrode metal and the upper surface of the base electrode extraction region are removed using an anisotropic dry etching method. forming a protective film made of the material on the side walls of the collector electrode metal and the side walls of the collector portion protruding from the upper surface; forming an external base region; depositing the base electrode metal from above; 1. A method for manufacturing a heterojunction bipolar transistor, comprising at least the step of forming a base electrode in a peripheral area immediately below the umbrella consisting of a metal umbrella or collector electrode metal and the side wall. (2) The collector electrode metal is formed by lift-off to the size of the collector, or by vapor-depositing the collector electrode metal on the entire surface and removing the peripheral part of the collector by etching, and etching using the collector electrode as a mask to form a striped shape. A method for manufacturing a heterojunction bipolar transistor according to claim 1, characterized in that a protruding region is formed. (3) As the multilayer structure material, use a zinc blend type material epitaxially grown in the <001> direction or a multilayer structure material consisting of a zinc blend type material and a diamond type material, and align the extension direction of the striped protrusions with the surface of the multilayer structure material. The heterojunction bipolar according to claim (2), characterized in that a silicon oxide or silicon nitride thin film is used as a protective film provided in the <100> direction or <110> direction and forming the side walls. Method of manufacturing transistors. (4) selectively removing the material for forming the heterojunction bipolar transistor in a portion that will become the collector region;
and providing a temporary collector made of a material that is not substantially corroded by the etching solution of the underlying material, etching the temporary collector using the temporary collector as a mask, and then covering the entire surface with photoresist and exposing the upper part of the temporary collector by dry etching, The method for manufacturing a heterojunction bipolar transistor according to claim 1, wherein the temporary collector is then removed, and after the removal, a collector electrode metal is formed by lift-off. (5) As a multilayer structure material, use a zinc blend material epitaxially grown in the <001> direction or a multilayer structure material consisting of a zinc blend material and a diamond material, and align the extension direction of the striped protrusions within the plane of the multilayer structure material. provided in the <100> direction or <110> direction of
The method for manufacturing a heterojunction bipolar transistor according to claim (4), further comprising using silicon oxide or silicon nitride as the protective film forming the sidewall. (6) As the multilayer structure material, use a zinc blend type material epitaxially grown in the <001> direction or a multilayer structure material consisting of a zinc blend type material and a diamond type material, and set the extension direction of the striped projections to the surface of the multilayer structure material. The method for manufacturing a heterojunction bipolar transistor according to claim (1), wherein the heterojunction bipolar transistor is provided in the <110> direction or the <100> direction. (7) A method for manufacturing a heterojunction bipolar transistor according to claim (1), characterized in that a silicon oxide or silicon nitride thin film is used as the protective film forming the sidewall.